1. Field of the Invention
The present invention relates to photometric analysis, and in particular to a novel method and apparatus for photometrically measuring chlorine dioxide concentrations in a stream.
2. Description of Related Art
Chlorine dioxide in solutions at various concentrations is useful as a bleaching agent for pulp used in the manufacture of white paper, or to oxidize and disinfect in a variety of applications. One such notable application, is the treatment of drinking water where limited amounts of chlorinated chemicals such as sodium chlorite is desired.
In a chlorine dioxide generator, for example, the addition of the optimum quantities of sodium chlorite and chlorine results in a conversion to chlorine dioxide of almost 100% with almost non-detectable sodium chlorite and chlorine found therein. In order to meet the necessary safety standards and the stringent government regulations, it is of particular importance to detect changes in chlorine dioxide concentration and optimize the chlorine and sodium chlorite additions to achieve as high a rate of conversion to chlorine dioxide as possible.
On site generation of chlorine dioxide is common, as the solutions cannot be shipped or stored for long periods of time. Control of the generating process is needed to manufacture solutions with respective concentrations. The article "Continuous Monitoring for Control of Chlorine Dioxide Generators" written by R. S. Saltzman and published in "Instrumentation in the Pulp and Paper Industry," Volume 16, Section 609, Coden: IPPICO 16 (1975), Instruments Society of America, Research Triangle Park, North Carolina, describes a photometric analysis apparatus adapted to continuously monitor the output of a chlorine dioxide generator. These conventional analyzers employ incandescent light sources such as the ones disclosed in U.S. Pat. No. 4,152,073 (Zimmerman) issued on May 1, 1979 and U.S. Pat. No. 4,311,485 (Saltzman et al.) issued on Jan. 19, 1982).
Some of the disadvantages associated with these light sources is that they require more power, generate more heat and slowly deteriorate to the point of failure. Typically analyzers with incandescent light sources require warm up times of thirty minutes to a day. Therefore, the light is left in the on position to provide stability, and chopper wheels are utilized to obtain detector readings in the dark by blocking the light selectively.
Another drawback related to commercially available analyzers is that multiple interference filters, prisms, or gratings are necessary to generate monochromatic light beams. These types of interference filters are disclosed in U.S. Pat. No. 4,152,073 (Zimmerman) issued on May 1, 1979. In accordance with DeBeers law, monochromatic light is absorbed by chlorine dioxide and results in logarithmic changes in light intensity and detector responses.
To overcome the disadvantages of the prior art, it is an object of the present invention to provide an analyzer having blue and red light emitting sources (LED's) which can last up to ten years, provide a more stable light output and consume less energy (less than 76 mW). The analyzer allows the passing of light emitted from the blue diode directly through the chlorine dioxide solution and measures the response sensed by a detector without calorimetric filtering. The broad band emission of the blue light emitted overlaps a small portion of the chlorine dioxide light absorbing region. The overlap in the blue light emission and chlorine dioxide absorbance results in detector responses which are inversely linear to the chlorine dioxide concentration.
A further object of the present invention is to simplify the electrical requirements of the analyzer. Monochromatic light measurements afforded by commercially available analyzers result in logarithmic responses which must be converted to linear electrical readings. It is an object of the present invention to provide an inverse linear response to chlorine dioxide at high concentrations which simplifies amplification circuits and expands the chlorine dioxide measurement range.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended thereto.